Dissolution of regenerated cellulose with urea-alkali-stannate solvent



Patented Dec. 12, 1950 DISSOLUTION OF REGENERATED CELLU- LOSE WITH SOLVENT UREA-ALKALI-STAN NATE Charles L. Mantell, Manhasset, N. Y., assignor to United Merchants and Manufacturers, Inc Wilmington, Del., a corporation of Delaware No Drawing. Application May 10, 1949, Serial No. 92,514

10 Claims.

This invention relates to a solvent for rayon, sometimes referred to as artificial silk or regenerated cellulose.

A primary object of the invention is to provide a solvent useful over a relatively wide tempera ture range, by means of which regenerated cellulose, in whatever form, can be dissolved. Such a solvent has a Wide field of useful applications, such as to provide a solution of regenerated cellulose suitable for further use, as for finishing operations, or to remove regenerated cellulose Wherever desirable, as in stripping operations or in the production of design effects.

It'has heretofore been proposed (as in United States Patent No. 2,322,427, for example), to dissolve regenerated cellulose in an aqueous solution of sodium zincate. There are, however, several disadvantages inherent in such use of sodium zincate, among which are the low treating temperatures required, 1. e., not above C. and preferably below, involving the use of expensive refrigeration equipment and material. Following such treatment, the cellulose solution must then be aged for a considerable period before it is ready for use, entailing a loss of time. Furthermore, sodium zincate solutions have a restricted field of application, exhibiting solvency power for but a limited number of materials and being ineffective as to others. In addition, these solutions tend to be unusually viscous, and this condition becomes excessively pronounced as the cellulosic concentration is increased, thus causing handling disadvantages Attempts have been made to overcome the disadvantage of the low temperature requirements of the foregoing process but by the use of such excessive amounts of sodium zincate as to introduce other difiiculties.

According to the present invention, it is proposed to use caustic stannate-urea as the solvent to improve upon the heretofore used methods of dissolving regenerated cellulose, the improvement being particularly notable with respect to the increased solvent power, i. e., the time required to effect solution, and to the low Viscosity and increased clarity of the resulting solution, as will be shown. This solvent, i. e., caustic stannate plus urea, is useful at low temperatures, but it is especially advantageous in that it is highly effective at room temperature and up to about 120 F.

The solvent may be prepared by mixing together an aqueous solution of urea and an alkali metal stannate selected from the class consisting of sodium stannate and potassium stannate; or by adding stannic oxide to an aqueous solution of an alkali metal hydroxide selected from the class consisting of sodium hydroxide and potassium hyroxide, sodium stannate and potassium stannate respectively being formed, and then incorporating the urea. It is to be understood that in referring to the stannic oxide content of the solution, it is intended to include the oxide added as such or as comprised in the alkali metal stannate added to the solution or formed therein. The amount of urea may be varied from about 1 to about 20% by weight, preferably from about 5 to 12%. Stannic oxide, whether added as such or in the form of the stannate, may be present in amounts ranging from about 1.3 to about 2.2% by weight calculated as stannic oxide. The caustic may be varied from about 8 to about 19% by Weight or more, although the use of higher concentrations of caustic generally does not justify the added expense involved. If sodium hydroxide is employed as the caustic, a preferred concentration from about 3 to about 15%; for potassium hydroxide, a preferred range is from about 12 to about 19%, Below the minimum concentrations given, solvency power is affected; while above maximum concentrations, there is no worthwhile improvement in results. A particularly good solvent is one composed of 1.3 to 1.8% stannic oxide, 10% sodium hydroxide, 10% urea, and the remainder Water.

The Weight relations of the sodium stannate referred to in the examples following are based on the commercial material known as sodium stannate which contains about 44% of SD02, rather than on the compound represented by the formula NazSnOs. Material of other concentrations of Sn02 may, of course, be employed, care being had to maintain an overall amount of SnOz of between about 1.3 and about 2.2%.

Compounds which, when added to a caustic stannate solution, hydrolyze to form urea, may be used in making up the solvent. Such compounds may include for example, cyanamide, guanidine, guanylurea, etc. In the premises, it will be understood that the term urea as used herein is intended to include urea per se and also compounds which produce urea as in the foregoing manner.

Any type of product or Waste composed of regenerated cellulose may be treated with the solvent of this invention. Regenerated cellulose materials include, for example, yarns, threads, cloth, clippings, cord Waste, comber waste, lacings, strings, tire cord, or other forms of regenerated cellulose made by the Viscose, Bemberg, or any other processes.

r 3 As already mentioned, the solvent is highly effective at room temperatures and thus eliminates the necessity for refrigeration material or equipment. After the cellulosic materials have been dissolved, the solutions so obtained are ready for immediate use. No ageing or ripening to reduce thu viscosity is required, as the'solutions exhibit good viscosity characteristics at various concentrations of solute.

The effectiveness of the solution is indicated by the following examples:

Example I A solvent was made up containing grams urea, 4 grams sodium stannate, and 10 grams A solution was prepared containing 10 grams of caustic soda and 3 grams of sodium stannate per every 100 cc. of solution, and to 100 cc. portions of this solution there was added from 1 gram to grams of urea in 15 different solutions. Another 100 cc. portion was taken to which no urea was added. Three gram samples of semi-coarse rayon waste were then added to each of these solutions. It was noticed that as the amount of urea was increased, the rayon solutions improved in clarity and showed lowered viscosities. Viscosities were determined on all of these solutions after standing for 10 minutes and are tabulated Viscosity determinations were made by means of a Stormer viscosimeter; time of 100 revolutions was measured in seconds using a GOO-gram load at room temperature.

Example III A clarity test was made as follows: a solution containing 10 grams of caustic soda, 3 grams of sodium stannate, 10 grams of urea, and 3 grams of dissolved rayon waste was prepared and found to be transparent enough to reveal a black letter the rayon required on a paper pad, the letter being A of an inch high and of an inch wide. A two-inch column of solution was employed. The letter was entirely invisible through a similar solution containing no urea.

It will be appreciated that the improved viscosity and clarity characteristics of the ureastannate solutions of regenerated cellulose are indicative of the increased solvency power of the olvent.

In applying the solvent, regenerated cellulose as contained in any type of fabric, yarn, or filament, either new or in the form of waste material, may be recovered and reduced to a usable form. Soiled wastes need not be expressly purified if their contaminants are permissible in the application of the resulting solution. If the cellulosic material is permitted to swell a short time in the caustic stannate solution prior to adding the urea, a uniform solution may be rapidly produced. The solution resulting may be used directly as a finishing composition for various textile materials.

Cloth to be finished is passed through the solution and then the cellulose is reprecipitated on the fibers of the cloth by means of a coagulant,

such as hot or cold water or dilute acid, and

the cloth is rinsed and dried. A 3-4=% solution of regenerated cellulosic material in the solvent has been found very suitable, and a useful concentration range is l to 6%.

The solvent may also be employed to salvage cloth made of material other than rayon and having a finish of regenerated cellulose. Where such finish is no longer desirable, it may be stripped from the cloth by means of the solvent without substantially affecting the cloth itself. Inert pigments or fillers forming a part of the finish are also removed in the stripping operation. A variety of finishes can thus be stripped from textile cloths, the conditions to be observed being that the finish be substantially composed of regenerated cellulose and soluble in the solvent and that the cloth be substantially insoluble in the solvent. Stripping may be aided by mechanically working the cloth through the solvent and brushing to loosen the adhering finish. The cloth may then be washed with more solvent and finally with water. A counter-flow stripping and washing system, in which the cloth travels in a direction counter-current to the flow of solvent and wash water, and in which the solvent may be used until it is completely spent, may be employed to advantage.

This application is a continuation-in-part of co-pending application Serial Number 616,455, filed September 14, 1945 now abandoned.

It may be noted that instead of the urea or urea-forming compounds as previously described, oth r substances may replace that factor or component as, for examples, the alkali metal thiocyanates; sodium thiocyanate, potassium thiocyanate or ammonium thiocyanate, and the polyamines; ethylene diamine or hexamethylenetetramine.

In the light of the foregoing description, the

following is claimed:

1. Solvent for regenerated cellulose comprising an aqueous solution of about 8 to about 19% by weight of an alkali metal hydroxide selected from the class consisting of sodium hydroxide and potassium hydroxide, about 1 to about 20% by weight of urea, and alkali metal stannate selected from the class consisting of sodium stannate and potassium stannate in an amount equivalent to from about 1.3 to about 2.2% by weight of stannic oxide.

2. Solvent for regenerated cellulose comprising an aqueous solution of from about 8 to about 15% by weight of sodium hydroxide, about 1 to about 20% by weight of urea, and sodium stannate in an amount equivalent to from about 1.3 to about 2.2% by Weight of stannic oxide.'

3. Solvent for regenerated cellulose comprising an aqueous solution of from about 12 ,to about b 19% by weight of potassium hydroxide, about 1 to about 20% by weight of urea, and potassium stannate in an amount equivalent to from about 1.3 to about 2.2% by weight of stannic oxide.

4. Solvent for regenerated cellulose comprising an aqueous solution of about 10% by weight of sodium hydroxide, about 10% by weight of urea, and sodium stannate in an amount equivalent to from about 1.3 to about 1.8% by weight of stannic oxide.

5. Method of removing regenerated cellulose from textile material containing the same which comprises treating such material with an aqueous solution of about 8 to about 19% by weight of an alkali metal hydroxide selected from the class consisting of sodium hydroxide and potassium hydroxide, about 1 to about 20% by weight of urea, and alkali metal stannate selected from the class consistin of sodium stannate and potassium stannate in an amount equivalent to about 1.3 to about 2.2% by Weight of stannic oxide.

6. Method which comprises treating regenerated cellulose with an aqueous solution of about 8 to about 19% by Weight of an alkali metal hydroxide selected from the class consisting of sodium hydroxide and potassium hydroxide, about 1 to about 20% by Weight of urea, and alkali metal stannate selected from the class consisting of sodium stannate and potassium stannate in an amount equivalent to about 1.3 to about 2.2% by weight of stannic oxide.

7. Composition of matter in the form of an aqueous solution comprising about 8 to about 19% by Weight of an alkali metal hydroxide selected from the class consisting of sodium hydroxide and potassium hydroxide, about 1 to about 20% by weight of urea, alkali metal stannate selected from the class consisting of sodium stannate and potassium stannate in an amount equivalent to from about 1.3 to about 2.2% by weigi. t of stannic oxide and about 1 to about 6% by weight of regenerated cellulose.

8. Composition of matter which comprises an aqueous solution of about 10% by weight of sodium hydroxide, about 10% by weight of urea, sodium stannate in an amount equivalent to from about 1.3 to about 1.8% by weight of stannic oxide and about 3% by weight of regenerated cellulose.

9. Composition of matter which comprises an aqueous solution of about 8 to about 15% by weight of sodium hydroxide, about 1 to about 20% by weight of urea, sodium stannate in an amount equivalent to from about 1.3 to about 2.2% by weight of stannic oxide and about 1 to about 6% by weight of regenerated cellulose.

10. Composition of matter which comprises an aqueous solution of about 12 to about 19% by weight of potassium hydroxide, about 1 to about 29% by Weight of urea, potassium stannate in an amount equivalent to from about 1.3 to about 2.2% by weight of stannic oxide and about 1 to about 6% by weight of regenerated cellulose.

CHARLES L. MANTELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. SOLVENT FOR REGENERATED CELLULOSE COMPRISING AN AQUEOUS SOLUTION OF ABOUT 8 TO ABOUT 19% BY WEIGHT OF AN ALKALI METAL HYDROXIDE SELECTED FROM THE CLASS CONSISTING OF SODIUM HYDROXIDE AND POTASSIUM HYDROXIDE, ABOUT 1 TO ABOUT 20% BY WEIGHT OF UREA, AND ALKALI METAL STANNATE SELECTED FROM THE CLASS CONSISTING OF SODIUM STANATE AND POTASSIUM STANNATE IN AN AMOUNT EQUIVALENT TO FROM ABOUT 1.3 TO ABOUT 2.2% BY WEIGHT OF STANNIC OXIDE. 